JP5003733B2 - Single crystal growth method - Google Patents

Description

  The present invention relates to a single crystal growth method, in particular, a horizontal magnetic field application CZ method (HMCZ) in which a single crystal is pulled from the raw material melt while applying a horizontal magnetic field to the raw material melt in the crucible by coils arranged oppositely across the crucible. This method relates to a single crystal growth method called Horizontal Magnetic field applied CZ method.

  There are various types of methods for producing a silicon single crystal used for a semiconductor substrate, and the CZ method (Czochralski method) which is a rotational pulling method is widely used industrially. In the production of a silicon single crystal by the CZ method, a crystal growth apparatus as shown in FIG. 7 is used. This crystal growth apparatus includes a crucible 1 that contains a silicon melt 13 that is a raw material melt, and an annular resistance heater 2 disposed outside the crucible 1. The crucible 1 has a double structure in which an inner quartz crucible 1a and an outer graphite crucible 1b are combined, and is placed on a support shaft 6 that can be moved up and down and rotated. The crucible 1 is housed in a chamber (not shown) together with an outer heater 2 and the like.

  In operation, the seed crystal 15 suspended on the pulling shaft 5 made of a wire or the like is immersed in the silicon melt 13 in the crucible 1. Then, the silicon single crystal 12 is grown under the seed crystal 15 by raising the pulling shaft 5 while rotating the crucible 1 and the pulling shaft 5 in the reverse direction or the same direction to pull up the seed crystal 15. The crucible 1 is gradually raised in order to offset the lowering of the liquid level of the silicon melt 13 accompanying the growth of the silicon single crystal 12 and maintain the liquid level constant.

  More specifically, the crucible is prepared by melting the solid material in the crucible 1 with the heater 2 disposed outside the crucible 1 in a state where the pressure in the chamber is reduced to a predetermined degree of vacuum and maintained in a predetermined inert gas atmosphere. A silicon melt 13 is formed in 1. After the seed crystal 15 is immersed in the raw material melt 13, the seed crystal 15 is narrowed down to about 3 mm in diameter in order to remove dislocations originally contained in the seed crystal 15 and dislocations introduced by heat shock during landing. . After the seed drawing process (necking process), the straight body part is started to be pulled up through a shoulder forming process (diameter increasing process) in which the diameter is gradually increased to a predetermined diameter.

  In the production of such a silicon single crystal by the CZ method, as described above, it is customary to use a quartz crucible as a container for containing a raw material melt. When this quartz crucible comes into contact with the silicon melt, it reacts with the melt and releases oxygen. A part of the oxygen released into the melt is taken into the single crystal during pulling, and has various effects on the quality of the silicon wafer. For this reason, control of the oxygen concentration in the silicon melt is an important technique.

  As one of methods for controlling the oxygen concentration in the raw material melt in the CZ method, there is a magnetic field applied CZ method (MCZ method: Magnetic field applied CZ method). In this method, by applying a magnetic field to the raw material melt in the crucible, melt convection in the direction perpendicular to the magnetic field lines is suppressed, and oxygen elution is suppressed. There are various types of magnetic field application methods, and the practical application of the HMCZ method in which a magnetic field is applied in the horizontal direction is in progress.

  As shown in FIGS. 8 and 9, the crystal growth apparatus used in the HMCZ method is a set of coils 30a and 30b that are symmetrically arranged opposite to each other with the chamber interposed outside the chamber 7 in order to apply a magnetic field. It has. The chamber 7 includes a large-diameter cylindrical main chamber 7a that accommodates a hot zone such as the crucible 1, and a small-diameter long pull chamber 7b that is stacked on the center of the main chamber 7a to accommodate the grown single crystal. The pair of coils 30a and 30b are arranged on the outside of the main chamber 7a so as to be coaxially arranged on a horizontal line intersecting with the center of the chamber. On the other hand, in addition to the crucible 1 and the heater 2, a heat insulating material 8a is disposed along the inner surface of the peripheral wall of the main chamber 7a, and a heat insulating material 8b is disposed along the bottom surface inside the main chamber 7a. ing.

  The shape of the coil that forms the horizontal magnetic field is usually a laterally annular shape, but Patent Document 1 also describes a coil that is curved in a saddle shape along the outer shape of the main chamber. The position of the line connecting both coil centers is usually set to a level that substantially matches the surface of the raw material melt in the crucible, as described in Patent Document 2, but is applied to the raw material melt. For the purpose of improving the uniformity of the magnetic field strength, Patent Document 3 also describes a technique of positioning below the surface of the raw material melt, specifically, near the center in the depth direction of the raw material melt in the crucible. Yes. In this specification, a line connecting both coil centers is referred to as a coil center line, and is indicated by CC in FIG.

JP-A-8-333190 US Pat. No. 4,565,671 Japanese Patent No. 2949437

  By using a coil that is curved in a saddle shape in the HMCZ method, it is possible to generate a magnetic field of the same strength with a small magnetomotive force and to reduce the size of the coil, compared to the case of using a planar normal coil. . However, on the other hand, there are the following problems.

  When the HMCZ method using a saddle-type coil is applied to pulling a large-diameter single crystal having a diameter of 200 mm or more with a large-diameter crucible having an inside diameter of 500 mm or more, a phenomenon peculiar to a saddle-type coil that the crystal diameter suddenly increases during the pulling. It was found to occur. When such a sudden increase in the crystal diameter occurs, the desired crystal quality cannot be obtained, and the pulling operation itself may be impossible. For this reason, in the HMCZ method using a saddle type coil, it is an important technical problem to prevent the phenomenon of rapid increase in crystal diameter.

  In addition, regardless of the shape of the coil, it is desirable that the rotation speed of the crucible be low in the HMCZ method. This is because in the HMCZ method, when the crucible rotation speed increases, the action of the melt to rotate with the crucible and the action of the melt to stop due to the influence of the magnetic field occur at the same time. This is because problems such as deterioration of the in-plane distribution of oxygen concentration occur. Because of this problem, a lower crucible rotational speed adopted in the HMCZ method is desirable.

  However, the crucible rotation speed is one of the important factors for controlling the oxygen concentration. Increasing the crucible rotation speed tends to increase the oxygen concentration in the crystal. By increasing the crucible rotation speed in the latter half of the crystal growth, An operation for making the oxygen concentration uniform in the crystal axis direction is performed. For this reason, there is a problem that the in-plane distribution of the oxygen concentration deteriorates in the latter half of the crystal growth. For this reason, development of a technique capable of increasing the oxygen concentration with high responsiveness without increasing the crucible rotation speed is awaited.

  An object of the present invention is to provide a single crystal growth method that prevents a sudden increase in crystal diameter during pulling, which is a problem in the HMCZ method using a saddle coil, and enables stable crystal pulling. Another object of the present invention is to provide a single crystal growth method capable of increasing the oxygen concentration without increasing the crucible rotation speed.

  The present inventors investigated and examined various factors affecting the rapid increase phenomenon for the purpose of preventing the rapid increase phenomenon of the crystal diameter during pulling, which is a problem in the HMCZ method using a saddle coil. As a result, the following facts were found.

  Even in the same HMCZ method, when a planar normal coil is used, a crystal diameter sudden increase phenomenon does not occur even at a coil position where a crystal diameter rapid increase phenomenon occurs when a saddle type coil is used. That is, the sudden increase in crystal diameter is a phenomenon that is inherent when a saddle coil is used. Although the detailed reason is unknown, it is thought that the difference of the magnetic flux distribution shape when using each coil has influenced.

  This rapid increase in crystal diameter is influenced by the amount of melt in the crucible, the number of revolutions of the crucible at that time, and the distance of the coil center line from the melt surface. That is, the sudden increase in crystal diameter occurs when the amount of residual liquid in the crucible satisfies the specific relationship between the number of revolutions of the crucible, and this relationship increases as the amount of residual liquid in the crucible decreases. The crucible rotation speed causing the rapid increase phenomenon is reduced. This relationship is influenced by the distance from the melt surface of the coil center line. The larger the distance, that is, the lower the coil center line from the melt surface, the more rapidly the crystal diameter increases. Tend to be.

  FIG. 3 is a chart showing conditions for rapidly increasing the crystal diameter when a quartz crystal with an inner diameter of 750 mm and a single crystal with a diameter of 300 mm is pulled up. The horizontal axis represents the amount of liquid remaining in the crucible, and the vertical axis represents the number of revolutions of the crucible. ing. As can be seen from the figure, the smaller the amount of residual liquid in the crucible, the sharper the crystal diameter increases at a lower crucible rotational speed. On the other hand, the rotational speed at which the crystal diameter rapidly increases is the position of the coil center line. Decreases as it falls. As a result of further investigation based on such a relationship, as long as the coil center line is at a position lower than the melt surface by 100 mm or more, there is no limitation on the amount of melt that can be filled in the crucible. It was found that there was no sharp increase in crystal diameter even at the crucible rotation speed.

  FIG. 4 is a comparison of oxygen concentrations at a crystal length of 200 mm when the distance from the melt surface to the coil center line is changed under the pulling conditions described above. It can be seen that when the same oxygen concentration parameters (crucible speed, furnace pressure, inert gas flow rate, etc.) are used, the oxygen concentration also changes when the center line position of the saddle coil is changed. More specifically, the lower the center line position of the saddle coil, the higher the oxygen concentration. As a result, it is possible to increase the oxygen concentration while keeping the rotational speed of the crucible at a low level, and the deterioration of the in-plane distribution of the oxygen concentration due to the increased rotational speed of the crucible is avoided.

The single crystal growth method of the present invention has been completed on the basis of such knowledge, and a horizontal magnetic field is applied to the raw material melt stored in the crucible in the chamber by the coils arranged opposite to each other across the crucible. In the single crystal growth method for pulling a single crystal from the raw material melt, the shape of the coil is a saddle shape that is curved along the outer shape of the chamber, and the center line of the coil is the raw material melt in the crucible. It is set at a position 120 to 180 mm away from the surface of the liquid in the depth direction, the magnetic field strength applied by the coil is 3000 Gauss, and the rotation speed of the crucible is 1.5 to 3 rpm .

In single crystal growth method of the present invention, by the distance from the surface of the material melt to the coil center line below it is set on 1 300 mm or more (120~180mm), related to the residual amount of liquid in the crucible In addition, regardless of the number of revolutions of the crucible, the phenomenon of a sharp increase in crystal diameter that is peculiar when a saddle coil is used is avoided. That is, when the distance from the surface of the material melt to the coil center line beneath it is less than 1 300 mm, even if the center line of the coil below the surface of the raw material melt is located, the residual liquid in the crucible Depending on the amount and the number of rotations of the crucible, there is a concern that a phenomenon of a rapid increase in crystal diameter may occur.

The upper limit of the distance is preferably 200 mm or less. This is because the distance from the surface of the raw material melt to the coil center line below it depends on the coil size and the crucible size, but if the coil center line is located below the surface of the melt, the magnetic flux in the melt This is because it is not preferable that the coil center line is lowered too much because the horizontal distribution of the coil tends to be disturbed and dislocations tend to occur. The present invention shall be the 120~180mm the range of the distance.

In the single crystal growth method of the present invention, the coil center line is set at a position 100 mm or more (120 to 180 mm) away from the surface of the raw material melt in the crucible in the depth direction. As a result, the oxygen concentration can be increased without increasing the number of revolutions of the crucible. As a result, the deterioration of the in-plane distribution of the oxygen concentration due to the increase in the number of revolutions of the crucible is prevented. Also, if the coil center line is moved in the vertical direction, the oxygen concentration control parameters other than the coil position (crucible rotation speed, furnace pressure, inert gas flow rate, etc.) do not change significantly, Control becomes possible.

  The single crystal growth method of the present invention is used to pull a large-diameter single crystal having a diameter of 200 mm or more using a large-diameter crucible having an inner diameter of 500 mm or more, which is likely to cause a rapid increase in crystal diameter even in the HMCZ method using a saddle coil. It is particularly effective.

  A technique for positioning the coil center line below the surface of the raw material melt is known from Patent Document 3 in a normal HMCZ method using a planar coil. However, this technology aims to improve the uniformity of the magnetic field strength applied to the raw material melt, and prevents the sudden increase in crystal diameter, which is a problem inherent to the HMCZ method using a saddle coil. Does not make any suggestion.

The single crystal growth method of the present invention can reduce the size of the coil by using a saddle type coil. In addition, the center line of the saddle coil is set at a position that is 100 mm or more (120 to 180 mm) away from the surface of the raw material melt in the crucible in the depth direction, thereby causing a problem in the HMCZ method using the saddle coil. This prevents the sudden increase in crystal diameter during pulling and enables stable crystal pulling. Further, avoided by setting the coil center line of this, it is possible to increase the oxygen concentration without increasing the crucible rotation speed, the in-plane distribution deterioration of the oxygen concentration in question when the increased number of crucible rotations in HMCZ method There is also an effect that can be done.

It is a schematic cross section of a crystal growth apparatus suitable for carrying out the single crystal growth method of the present invention. It is a top view of the crystal growth apparatus. It is a graph which shows the generation | occurrence | production conditions of the crystal diameter rapid increase phenomenon. It is a graph which shows the relationship between the distance from a melt surface to a coil centerline, and the oxygen concentration in a crystal | crystallization. It is a graph which shows oxygen concentration distribution of a crystal axis direction about the case where the distance from a melt surface to a coil centerline is 50 mm and 150 mm. It is a graph which shows oxygen concentration distribution of a crystal axis direction about the case where the distance from a melt surface to a coil centerline is 50 mm and 150 mm. It is a conceptual diagram of the CZ method. It is a schematic cross section of the crystal growth apparatus used for HMCZ method. It is a top view of the crystal growth apparatus.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a crystal growth apparatus suitable for carrying out the single crystal growth method of the present invention, and FIG. 2 is a plan view of the crystal growth apparatus.

  The present crystal growth apparatus includes a cylindrical main chamber 7a as a chamber 7 and an elongated cylindrical pull chamber 7b concentrically stacked thereon. A crucible 1 is disposed in the center of the main chamber 7a. The crucible 1 includes an inner quartz crucible 1a and a graphite holding crucible 1b arranged outside the crucible 1 and is placed on a support shaft 6 called a pedestal via a tray. A heater 2 is disposed outside the crucible 1. A heat insulating material 8 is further disposed in the main chamber 7a. The heat insulating material 8 includes a first heat insulating material 8a disposed along the inner surface of the peripheral wall of the main chamber 7a and a second heat insulating material 8b disposed along the bottom surface of the main chamber 7a.

  On the other hand, a pulling shaft 5 made of a wire is suspended in the pull chamber 7b through the pull chamber, and a seed crystal 15 is attached to the lower end thereof. The pulling shaft 5 is rotated and pulled up by a rotary winding mechanism (not shown) provided on the pull chamber for pulling the crystal.

On the other hand, on the outside of the main chamber 7a, a pair of coils 30a and 30b with the center line oriented in the horizontal direction are symmetrically opposed to each other across the main chamber. These coils 30 a and 30 b constitute a superconducting magnet that generates a horizontal magnetic field at the crucible position in the main chamber 7 a, and are coaxially arranged on a horizontal line that intersects the vertical center line of the chamber 7. The coils 30a and 30b are saddle-shaped coils that are curved in the horizontal direction along the outer shape of the main chamber 7a. At least during pulling, the coil center that connects both coil centers by a lifting mechanism (not shown). line C-C is to be located Toko filtered away over 100mm from the surface of the melt in the crucible 1 downward, its height is adjusted.

  Next, a method for growing a silicon single crystal having a diameter of 300 mm using the present crystal growth apparatus will be described.

  The inside of the chamber 7 was depressurized to 25 Torr, and Ar was introduced into the chamber 7 as an inert gas at a flow rate of 100 L / min. Then, the silicon raw material for crystal and the boron as an impurity filled in the crucible 1 were melted by the heater 2. Thereafter, the seed crystal 15 was immersed in the silicon melt 13 in the crucible 1, and the single crystal 12 was grown in the order of the neck portion 12a, the shoulder portion 12b, and the straight body portion 12c. The magnetic field intensity by the coils 30a and 30b was 3000 Gauss (0.3 Tesla). The target pull-up length of the straight body 12c is 1150 mm.

For comparison, the surface of the silicon melt 13, the coil 30a of the underlying, the distance L to the center line C-C of 30b, is set to 100mm smaller than 50 m m, was subjected to crystal growth. When the number of rotations of the pulling shaft 5 during the pulling of the straight body part 12c / the number of rotations of the crucible 1 was set to 8 rpm / 3 rpm, a sharp increase in crystal diameter occurred when the length of the straight body part was 120 mm. When the number of rotations of the pulling shaft 5 during the pulling up of the straight body 12c / the number of rotations of the crucible 1 is set to 8 rpm / 1.5 rpm, the crystal diameter rapidly increases when the length of the straight body having a small residual liquid amount is 580 mm. Occurred.

On the other hand, the distance L from the surface of the silicon melt 13 to the center line C-C of the coils 30a and 30b below it was set to 150 mm larger than 100 mm, and crystal growth was performed under the same rotation conditions. . Under any rotation condition, the crystal diameter did not increase rapidly until the crystal growth was completed.

  In addition, when the distance L from the surface of the silicon melt 13 to the center line C-C of the coils 30a and 30b below is 50 mm and 150 mm, the crystal is grown under the two types of rotation conditions described above. The oxygen concentration was investigated. The results are shown in FIGS.

As can be seen from both figures, the oxygen concentration increases as the number of revolutions of the crucible increases. On the other hand, the oxygen concentration decreases by lowering the coil center line when the number of revolutions of the crucible is 3 rpm or 1.5 rpm. To rise. Specifically, when the coil center line is set at 150 mm from the melt surface, it is 2 to 3 × 10 ¹⁷ atoms / cc (old ASTM) when the crucible rotation speed is 3 rpm than when the coil center line is 50 mm. When the crucible rotation speed is 1.5 rpm, the oxygen concentration increases 1.5 to 2 × 10 ¹⁷ atoms / cc (old ASTM).

  In the HMCZ method, when the rotation speed of the crucible increases, the melt tends to rotate with the crucible and the melt tries to stop due to the influence of the magnetic field, so the melt becomes unstable. . For this reason, the crucible rotation speed adopted in the HMCZ method is desirably lower. When the center line of the saddle coil is lowered, the oxygen concentration increases, so that the oxygen concentration can be made uniform in the crystal axis direction without increasing the crucible rotation speed in the latter half of the crystal growth.

According to the single crystal growth method of the present invention, the coil can be reduced in size by using the saddle type coil. In addition, the center line of the saddle coil is set at a position that is 100 mm or more (120 to 180 mm) away from the surface of the raw material melt in the crucible in the depth direction, thereby causing a problem in the HMCZ method using the saddle coil. This prevents the sudden increase in crystal diameter during pulling and enables stable crystal pulling. Further, avoided by setting the coil center line of this, it is possible to increase the oxygen concentration without increasing the crucible rotation speed, the in-plane distribution deterioration of the oxygen concentration in question when the increased number of crucible rotations in HMCZ method There is also an effect that can be done. Therefore, the single crystal growth method of the present invention is a very useful technique in the field of semiconductor substrate materials.

1 crucible, 2 heater, 5 pulling shaft, 7 chamber, 12 single crystal, 13 raw material melt, 15 seed crystal, 30a, 30b coil

Claims (1)

In the single crystal growth method of pulling a single crystal from the raw material melt while applying a horizontal magnetic field to the raw material melt accommodated in the crucible in the chamber by a coil arranged opposite to the crucible, the shape of the coil Is a saddle shape that is curved along the outer shape of the chamber, and the center line of the coil is set at a position 120 to 180 mm away from the surface of the raw material melt in the crucible in the depth direction. A method of growing a single crystal , wherein the applied magnetic field intensity is 3000 Gauss, and the crucible rotation speed is 1.5-3 rpm .

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